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The Effect of Inlet Tube Size on a Cone Shaped Flocculater
Shubha Bhar Taylor Britton
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Purpose and GoalsPurpose: To study the effects of influent tube size
on the growth and stability of the sludge blanket in a cone flocculator.
Goals:• Build up sludge blanket• Take turbidity values above blanket• Conduct Dimensional Analysis• Determine ideal tube size
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Velocity, Momentum, & Shear Velocity: too slow and the flocs settle,
too fast and they all wash out
Momentum: causes the interface between the sludge blanket and the overlying water to be unstable
Shear: Breaks up floc
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Hypothesis
We expected that the largest tube size will be most effective in producing the most stable sludge blanket for a given flow rate.
Expected points of failure:velocity = 0.2 m/s
shear = 0.1 Pa
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Set Up
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Flow Rates and DosageDose Rate and Concentrations
Alum Dose 50 mg/L
Clay 100 NTU
Flow 1:
Alum Concentration 12.5 g/L
Clay Concentration 12.2 g/L
Flow 2:
Alum Concentration 25 g/L
Clay Concentration 24.4 g/L
Flow RatesSludge Blanket Pump 20 mL/min
Flow 1:
Water Flow 100 mL/min
Alum Pump 0.46 mL/min
Clay Pump 1.65 mL/min
Flow 2:
Water Flow 200 mL/min
Alum Pump 0.46 mL/min
Clay Pump 1.65 mL/min
f f
a a c c w w f f cc
Q CQ C Q C Q C Q c C
Q
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Trials: Q = 100 mL/min
Trial 1: Pipe diameter = 0.635 cm (0.25 inch)Q = 100 mL/min
Trial 2: Pipe diameter = 0.953 cm (3/8 inch)Q = 100 mL/min
No sludge blanket formed!
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Trials: Q = 200 mL/min Trial 3: Pipe diameter = 0.953 cm (3/8 inch)
Sludge Blanket: 27 cm
Trial 4: Pipe diameter = 0.635 cm (0.25 inch)Sludge Blanket failure
Trial 5: Pipe diameter = 0.953 cm (3/8 inch)Sludge Blanket: 15 cm
Trial 6: Trial 4: Pipe diameter = 0.635 cm (0.25 inch)Sludge Blanket failure
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Turbidity Measurements: Trial 4Turbidity vs. Time: 1/2" pipe, 200 mL/min
0
1
2
3
4
5
6
7
8
9
0 5000 10000 15000 20000 25000 30000
Time (s)
Tu
rbid
ity
(NT
U)
Q = 200 mL/min, sludge blanket height = 27 cm,
pipe diameter = 0.953 cm
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Turbidity: Trial 5
Turbidity vs. Time: Sludge Blanket Growth
40
60
80
100
120
140
160
0 5000 10000 15000 20000 25000 30000
Time (s)
Tu
rbid
ity
(NT
U)
Q = 200 mL/min, sludge blanket height = 15 cm, pipe diameter = 0.635 cm
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Velocity CalculationsInner Tube Diameter (cm)
Q (mL/min)
Velocity out of pipe (m/s)
Velocity in Tank (m/s)
0.635 100 0.054 0.0083
0.953 100 0.024 0.0083
0.635 200 0.047 0.0166
0.935 200 0.105 0.0166
Mass balance used to determine velocity out of pipe and upward velocity in tank through the sludge blanket.
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ShearShear Values
Q (mL/min) Pipe Diameter Shear (Pa)
100 0.635 0.066
100 0.953 0.019
200 0.635 0.132
200 0.953 0.039
4
4 3
128 4
128 32
L Lw
Lw
gh gh ddQ
l l
h Q Q
l d g d
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Froude Number
Sludge Blanket Density = 1.00094 g/mL
Fr = 0.33
Froude number proportional to (inertial force) / (gravitational force)
Froude number is generally used to characterize flow,
• Fr numbers of less than 1 equal tranquil flow
• Fr numbers = 1 indicate critical flow
• Fr numbers greater than 1 indicate rapid flow.
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Reynolds NumberFlow is non turbulent!
jetVd
Re
Q = 200 mL/min
Pipe Diameter = 0.635 cm
Re = 56.6
Pipe Diameter = 0.953 cm
Re = 40
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Conclusions Our flow rates may have been too low Success may have been influenced by alum
spikes Building sludge blankets can be
unpredictable!